Method and system for determining curvature in fluid transmission pipelines

Abstract

A change in curvature or displacement of a section of submarine or subterranean fluid transmission pipeline is measured by traversing the pipeline with a pig having an onboard instrument package, including accelerometers and a longitudinal position measuring device comprising a magnetometer for counting the girth welds or other known magnetic anomalies along the section of pipeline to be measured. The accelerometers are mounted at the central longitudinal axis of the pig which is substantially coincident with the central longitudinal axis of the section of pipeline being measured so that the roll attitude of the pig does not influence the signals generated by the accelerometers. This arrangement precludes the requirement of mounting the accelerometers on a gyroscopic stabilized platform since the absolute position of the pig in space is not required, but primarily the change in curvature or displacement of the pipeline from a predetermined course is what is desired to be known. The pig weight is minimized and supporting structure is sufficiently stiff as to provide natural modes of vibration at frequencies higher than the frequencies of signals of interest as the pig traverses the pipe.

What I claim is: 
     
       1. A methof of determining a change in curvature of a section of subterranean or submarine pipeline comprising the steps of: providing pipeline pig means having onboard displacement sensing means mounted on said pig means in such a way that accelerations of said pig means due to changes in direction of the longitudinal axis of said section of pipeline may be sensed as said pig means traverses said section of pipeline without maintaining the roll attitude of said displacement sensing means in a predetermined position, said displacement sensing means comprising first and second accelerometer means mounted coaxial with the longitudinal central axis of said pig means and mounted for measuring accelerations normal to said longitudinal central axis and along axes forming an angle with each other, said pig means including position sensing means for determining the position of said pig means along the longitudinal axis of said section of pipeline and means for measuring the longitudinal velocity of said pig means along said longitudinal axis of said section of pipeline, said pig means including means operable for recording output signals from said displacement sensing means, said velocity sensing means and said position sensing means, and said pig means including support means for supporting said pig means to have its longitudinal central axis substantially coincident with the said longitudinal axis of said section of pipeline;   launching said pig means into said section of pipeline at a predetermined point on said section of pipeline and propelling said pig means through said section of pipeline while producing signals commensurate with the longitudinal velocity and position of said pig means in said section of pipeline and while producing signals indicative of lateral accelerations of said pig means due to curvature and/or change of longitudinal direction of said section of pipeline; and   retrieving said pig means at a retrieving station of said pipeline.   
     
     
       2. The method set forth in claim 1 including the step of: providing recording means on said pig means for recording signals related to said accelerations and the position of said pig means in said section of pipeline; and   recovering said recording means at said retrieving station so that recorded signals may be interpreted to determine displacement of said section of pipeline from a predetermined course.   
     
     
       3. The method set forth in claim 1, including the step of: supporting said pig means in said section of pipeline during its traversal therethrough without restraining said pig means from rolling about its own longitudinal axis in said section of pipeline;   and recording the angle of inclination of said pig means from a predetermined roll attitude of said means.   
     
     
       4. The method set forth in claim 1 wherein: the step of determining the position of said pig means includes providing means for measuring a change in the intensity of a magnetic field caused by girth welds between specific pipe sections of said section of pipeline to determine the location of said pig means at which changes in direction of said section of pipeline occur.   
     
     
       5. The method set forth in claim 1 wherein: said step of producing signals indicative of lateral accelerations of said pig means comprises producing a resultant acceleration signal and integrating said resultant acceleration signal to provide a resultant displacement signal.   
     
     
       6. The method set forth in claim 1, including the step of: providing means for determining the roll attitude of said pig means during traversal through said section of pipeline, and recording said roll attitude while recording any output signal generated by said displacement sensing means.   
     
     
       7. A method for determining a change in curvature of a section of generally cylindrical fluid transmission pipeline, said section of pipeline including a plurality of end-to-end connected pipe sections defining said section of pipeline and having a central longitudinal axis, said method comprising the steps of: providing a pipeline pig having means for supporting itself in said section of pipeline, said pig including accelerometer means mounted for sensing accelerations along axes substantially normal to said central longitudinal axis, said accelerometer means being mounted with respect to said central longitudinal axis such that signals produced by said accelerometer means are substantially insensitive to the roll attitude of said pig during traversal through said section of pipeline, and said means supporting said pig providing for natural modes of vibration of said pig as it traverses said section of pipeline to be of a frequency substantially greater than the signal frequency indicating a change in curvature of said section of pipeline;   providing means for sensing the position of said pig with respect to a predetermined point on said section of pipeline when traversing said section of pipeline;   launching said pig at a first predetermined point on said pipeline and recording signals generated by said position sensing means and said accelerometer means during traversal of said pig through said section of pipeline to determine a change in curvature or displacement of said section of pipeline; and   retrieving said pig at a second predetermined point on said pipeline.   
     
     
       8. Apparatus for determining a change in curvature of a section of generally cylindrical fluid transmission pipeline having a central longitudinal axis, said apparatus comprising: a pipeline pig including a housing and means for supporting said housing in said section of pipeline, said pig including accelerometer means mounted in said housing for sensing accelerations along axes substantially normal to said longitudinal axis and means for generating signals indicating the longitudinal velocity of said pig along said section of pipeline; and   said means for supporting said housing comprising a plurality of spaced apart resilient support members having a stiffness such that the natural modes of vibration of said pig laterally with respect to said longitudinal axis, as said pig traverses said section of pipeline, are of a frequency substantially greater than the measured signal frequencies of a said accelerometer means and said means for indicating velocity to indicate a change in curvature of said section of pipeline.   
     
     
       9. Apparatus for measuring the curvature or displacement of at least a section of fluid transmission pipeline, said section of pipeline comprising a plurality of end-to-end connected generally cylindrical pipe sections, said apparatus comprising: a pipeline pig including a housing having an interior space, means for supporting said housing in said section of pipeline for traversal therethrough in a predetermined position with respect to the longitudinal axis of said section of pipeline and means for propelling said pig through said section of pipeline;   displacement sensing means mounted within said housing and with respect to said longitudinal axis of said section of pipeline and nonresponsive to the roll attitude of said pig during traversal through said section of pipeline for generating a signal indicating a change in curvature of said section of pipeline, said displacement sensing means comprising at least two accelerometers mounted for sensing accelerations along respective axes forming an angle with each other, said axes being substantially normal to the longitudinal axis of said section of pipeline, said accelerometers being mounted substantially coaxial with respect to said longitudinal axis of said section of pipeline;   means for measuring the velocity of said pig along said longitudinal axis of said section of pipeline;   means for determining the longitudinal position of said pig in said section of pipeline; and   means for recording signals generated by said displacement sensing means, said velocity measuring means and said means for determining the longitudinal position of said pig, whereby the location of and degree of change in curvature or displacement of said section of pipeline may be determined.   
     
     
       10. The apparatus set forth in claim 9 wherein: the axis of movement of one of said accelerometers is normal to the axis of movement of the other of said accelerometers.   
     
     
       11. The apparatus set forth in claim 9 including: clinometer means disposed in said housing for measuring the roll attitude of said pig during its traversal through said section of pipeline.   
     
     
       12. The apparatus set forth in claim 9 wherein: said position sensing means includes means for sensing a magnetic anomaly as said pig passes from one pipe section to another pipe section during its traversal through said section of pipeline.   
     
     
       13. The apparatus set forth in claim 9 including: means for positioning the center of gravity of said pig displaced from the longitudinal central axis of said section of pipeline when said pig is disposed therein for biasing said pig in a predetermined roll attitude during traversal of said pig through said section of pipeline.   
     
     
       14. The apparatus set forth in claim 13, including: means associated with said displacement sensing means for filtering out signals created by relatively high frequency vibrations of said pig with respect to said section of pipeline, and means for recording signals generated by said displacement means indicative of displacement of said section of pipeline from a predetermined attitude.